Process of preparing concentrated vat acids



r" "e -"a Patented Mar. 25, 1952 PROCESS OF PREPARING CON CENTRATED VAT ACIDS George N. Sandor, Mexico City, Mexico No Drawing. Application July 23, 1949, Serial No. 106,510

1 Claim.

The present invention relates to improvements in the preparation and use of vat dyes.

The use of vat dyes, the popularity of which is attributable to their excellent fastness, often involves difficulties in practice. The reason is that the vat dyes in their commercial form are insoluble in Water and that, therefore, the dyebaths have to be prepared by reducing the dyes in alkaline solution to the sodium salts of their leuco compounds and that they have to be kept in this not very stable condition during the whole dyeing process. This means that the preparation of the vats, as well as the whole dyeing process, has to be carefully supervised.

Apart from this, however, difficulties arise in the dyeing of certain textiles as a result of the colloidal state and unstable nature of the vats. Thus, for instance, closely woven fabrics and tightly twisted yarns, particularly mercerized cotton and staple fiber, are not suifioiently dyed out by the vatted dye. Due to the intense swelling of the cellulose fibers in the alkaline medium of the vats, the dyes cannot penetrate through the fiber stock.

To overcome this difficulty various processes have been proposed, some of which have been adopted in practice. A method which is widely applied is as follows: the dye in insoluble finely dispersed form is evenly distributed from a neutral aqueous medium on and in the fibers by impregnation, and it is then brought into solution by means of alkaline reducing baths and fixed by subsequent oxidation. This process can, however, only be successfully applied if specially prepared highly dispersed powder or paste dye are used and even then completely level and thorough dyeing is not achieved in particularly difiicult cases.

A substantial technical advance has been brought about by the water-soluble alkali salts of the sulfuric acid esters of the leuco compounds of vat dyes. These products make possible an even and thorough dyeing of the fibers, which had been unattainable by any other method of dyeing with vat dyes. Apart from the fact, however, that the complicated preparation and corre-conversion of these dyes on the fiber into their final stable form by splitting the esters and oxidizing the leuco compounds are also subject to considerable variations, which again strictly limits the possibilities of combining them. Further, their development requires strongly acid liquors and the presence of powerful oxidizing agents, so that the material of which the equipment is made must be highly resistant.

Most of the disadvantages mentioned can be overcome by the vat acid process, which is alsov well known. Thi process is carried out by vatting the dyes in the normal way and neutralizing or slightly acidifying the vats by the careful addition of acids in the presence of dispersing agents having preferably slight reducing-properties. In

this way colloidal solutions are obtained which have a very high degree of dispersion and excellent stability, being atroom temperature not very susceptible to oxidation by air. The dyes applied in this form to the fibers are developedin alkaline baths in a manner similar to the.

pigment process.

As a result of the complete lack of substantivity for cellulosic fibers, the possibilities of combining the dyes with one another are almost unlimited, while on the other hand, due to thehigh degree of dispersion of the vat acid solutions, which approaches true solubility, the distribution of the dyes on and in the fibers is completely even. I

However, while even the normal vat process requires very careful supervision, particularly as respondingly high cost of these products set certain limits to their use for reasons of economy, their practical application, in spite of all their advantages, involves difficulties too. For instance, the substantivity of these dyes varie and is also variously affected by changes of temperaturefrequently in opposite ways. This often causes unleveled dyeing or uneven edges when combinations of them are used. The conditions for the regards the preparation of the vat, this is even. more true of the vat acid process. Preparing the vat acid dye baths from alkaline vats is only possible with a thorough knowledge of the properties of the various vat dyes, their solubility, and the quantities of chemicals required in each instance because the various dyes react very differently under differentconditions. If the optimal temperatures and times for vatting and neutralization. are not rigidly maintained, over-reduction, hydrolysis, molecular rearrangement and crystallization may take place, which may produce structural changes of the dyestuif or precipitation and impair the shade and fastness of the obtained colors. All this has made the application of the known vat acid process all but impossible in a normal dyeing plant. These requirements of a specific dyeing technique, careful control of the pH and careful addition of the reactants are probably the reason why the vat acid process, despite its great theoretical advantages, could not replace so far the alkaline vat dyeing process to any noteworthy extent.

Moreover, the known vat acid process has serious limitations regarding the obtainable depth of color, which will be stated more in detail hereafter.

It is a principal object of the invention to provide vat acids in a form permitting to obtain concentrated solutions or dispersions of the same.

Another object of the invention is to provide vat acid solutions or dispersions of a high or any desired concentration adapted for dyeing textile fibers or goods of whatever composition.

Other objects and advantages will be apparent from a consideration of the specification and claim.

According to the invention, free vat acids are. prepared in concentrated stable, readily water: soluble form by mixing the paste or powder of a commercial vat dye with a relatively small amount of water, for instance in the proportions of 1 part'of dyestuff to 5 parts of water, and with the necessary reducing agents. In this way re, ductiontakes place though the vat dyestu'ff in its leuco form isnot actually dissolved-j The paste may be further concentrated by evaporating 'the water under reduced pressure, preferably at temperatures not exceeding 60-"l 0 C When this paste is then neutralized 'or slightly acidified in the presence or protective colloids, the resulting product which contains f-reevat acid in'high concentration becomes water soluble or is at least readily "emulsifiedwith water in'any proportion." Such concentrated solutions or dis} persions o'f'vat'ac'ids permit of dyeing textiles in a continuous manner in a single operation to any desired depth. 'They may be used for dyeing and printing fibrous materials of a great variety and open up new kinds of tinctorial uses.

' A's aprotective behold I may use any colloid compatible withthe solution of the leuco compounds or the vat acids, such as, for instance, condensation products of napthalene sulfonic acids with formaldehyde, fatty alcohol sulphonates, quarternary ammonium, sulphonium or phosphonium compounds, sodium lignin sulphonat'epand othersj The invention makes it possible to prepare in a simple and economic manner vat dyes in a stablefrea'dily water-soluble and high concen trated commercial form. A further advantage is that with the products according to the invention there are no limitations as to the depth of color obtainable because the paste-like or solid vat. acids can be dissolved in water to any desired concentration. Small amounts. of a weak or..mo dera .lv strong acid, e.g. tartaric acid or delta-gluconolactone may be added to the vat acid pastes or, powders in order to stabilize the i et q qr Some of the, advantages presented by the pro ducts 'of the, invention may .be better understood frdm' the, following consideration:

Dilute vat acid dispersions were the only form whiqh at a dsws c m c l sed her i b i lii in h swe d K e s eeure a acid process. They have the serious drawback of presenting solutions of a relatively low vat acid content since th e upper limit of concentration of the vat acid is controlled by the solubility o f the vet dyestuff Attempts to concentrate these dilute dispersions were not successful because it was notpo'ssib'le to removelarge amounts of water without partial reoxidation ofthe free leuco compounds. The solubility of many vat dyes, particularly of the anthraquinone series, is about '78 g./l. Therefore, the concentration of the vat acid contained in such solutions by neutralizing or acidifying the alkaline solution is of the same order of magniture, i. e., about .8 per cent. In the vat acid dyeing process, the depth of color obtainable is controlled by the amount of dye liquor which can be uniformly absorbed by the goods. Cotton goods, for instance, absorb 100 per cent of its dry weight; in other words, 1 kg. of the goods can retain only 1 kg. of the vat acid solution which contains, when obtained according to the known methods, about .8 per cent of dyestuff. The impregnated goods then contain per kg. 8 g. of vat acid calculated on its dry weight, i. e. about 0.8 per cent; this is the maximum depth obtainable in the vat acid process.

These considerations show that it is impossible with difficulty soluble vat dyes to obtain in the known vat acid process a depth of color of, for instance, 3 per cent, as is easily obtained in the alkaline vat dyeing process and as is often desir able for obtaining full shades.

This has been'a serious drawback of the vat acid dyeing process. This drawback is overcome by the new process according to the invention where solid vat acids or vat acid pastes are'employed as starting material. Using, for instance. a paste containing 16 per cent of a vat acid and dissolving 188 grams of such paste, i. e. 30 g. of free vat aeid in 1 litre of water, it will readily be seen that l kg. of the goods, absorbing 1 kg. of theliquor, will take up '30 g. of the dyestuif corresponding to 3 per cent of its weight. No vat acid dyeing process has been known heretobefore where such a high absorption and depth of the color could be obtained evenly and uniformly throughout the goods.

in the normal dyeing process, the dyer will often be required to dye compound shades with dyestuff; combinations. In the case of vat dyes he has been compelled either to prepare separate stockvats according to the different properties of the dyestuffs or to make a selection among the few dyestuffs having similar vatting properties and similar rates of dyeing. The latter procedure is often not possible because the few available combinations would not give the desired shade or uniform fastness. This drawback disappears when the new process is employed because the free vat acids can be mixed with each other and dissolved and used together in any desired concentration and combination.

Another disadvantage of the known vat and vat acid process consists in the difficulty or impossibility to obtain the desired shade with the first preparation of the dyebath. Therefore, it is often necessary to adjust the dyebath by addition of small quantities of dyestufi. This matching the shades is a delicate and time consuming procedure because it is not possible to add simply'a certain amount of the dyestuff but each timea new stock vat has to be prepared, which involves a repetition of the diificult manipulations with the inherent risk of changing the shade or'fastness of the color. According to the new dyeing process the dyebath can be adjusted without anyloss of time by simply dissolving an additional amount of precipitated free vat acid to the desired concentration and adding it to the dyeing bath.

The vat acid precipitates according to the invention are also very suitable for the normal vat dyeing process in caustic alkali reduction baths.

l leretobefore, the dyer h'ed to make the immune vat from the water insoluble vat dyestufi by preparing a stock vat and adding it to the working vat sharpened previously with sodium hydroxide and sodium hydrosulphite. All these lengthy manipulations become unnecessary when vat acid powder or paste is used. In this case, it is suflicient to introduce into the sharpened working vat the solution of a predetermined amount of vat acid. As the dyestuff is present in the reduced state and is converted at once in the alkaline bath into the substantive form, it is possible to start immediately with the dyeing proper. In this way, the dyeing process is simplified and shortened and becomes equal to the simplest dyeing process, i. e. the dyeing with direct dyestuffs.

From the foregoing, it will be seen that the new dyeing method overcomes the difficulties in the preparation of the vat acids which have opposed the introduction of the vat acid process in the dyeing art, and that the new method is susceptible of economical universal and simple application because it allows to prepare vat acid dyebaths in any desired concentration and combination of different vat dyestuffs.

The following examples will further illustrate how the invention may be carried out in practice, but the invention is not restricted to these examples. The parts are by weight unless otherwise stated.

EXAMPLE 1 DI-O-CHLOROBENZO-l.4-DIAMINOANTHRAQUINONE 100 parts of this dyestuif are vatted in the usual manner at a temperature of 60 C. in an aqueous solution containing 330 parts by volume of sodium hydroxide (36 B.), '75 parts of sodium hydrosulfite, 100 parts of the sodium salt of lignin sulphonic acid and 5,000 parts of water. The alkaline solution is neutralized with 138 parts by volume of formic acid (90%) dissolved in 50 parts of water and the resulting colloidal solution is freed by filtration from any vat scum and other impurities that may be present. The acid solution is then evaporated under reduced pressure of 60 mm. Hg. at a temperature of about 70 0., to give either a dry solid or a paste having a vat acid content of about 16%.

A dyebath is prepared by dissolving 600 grams of this paste at atemperature of 60 C. in 100 l. of water. Bleached mercerized poplin is impregnated with this solution on a two roller foulard, squeezed with a squeezing effect of 80%, and then dried in a hot flue. Then the impregnated goods passes through the chemical pad containing 20 cc. of NaOH of 36 B., 20 grams of sodium hydrosulfite, and 50 grams of sodium chloride.

Subsequently, the goods is brought into the steambox,'where the conversion into the sodium leuco form takes place immediately and the dyestufi is fixed on the fiber. The goods passes then into a washing machine where it is oxidized, rinsed, and soaped; finally, the goods is dried. The described process is far superior to the known dyeing methods when it is desired, for instance, to obtain with this dyestuif a very light beige shade on large quantities of mercerized poplin.

The conventional jig-dyeing process is less suitable because the obtained shade will vary from one batch to another due to the difficulty of maintaining exactly the same dyeing conditions ineach batch. Further, the production cost would be very high because of the large consumption of chemicals-pastel shades necessitate relatively very much larger quantities of caustic soda and sodium hydrosulfite than heavy shades-and because of the considerable labor cost which is necessary for this process.

The normal pigment padding process would be much more economical; however, it cannot be employed for the manufacture of very light shades because of the unavoidable formation of streaks. In such delicate gradation of shades, any irregularity in the size of the dispersed pigment particles, no matter how small it be, will result in specks of darker color.

These drawbacks are obviated by the vat acid padding process because of the fine dispersion of the vat acid approximately true solubility. This vat acid padding process allows of continuous working and full development in a few minutes. However, the preparation of vat acid dispersions has been difficult heretofore because certain vat dyes, of which di-o-chlorobenzo-1.4-diaminoanthraquinone is illustrative, tend to hydrolyze in the strongly alkaline vats and tosplit off chlorine atoms, which affects the shade and 'fastness of the color. A raise of temperature is particularly objectionable; the temperature should by no means exceed 50 C. which is necessary for quick vatting. These difficulties are completely overcome by the new vat acid process where a con.- centrated vat acid is first prepared and this concentrated vat acid composition is then used for preparing the dyebath.

EXAMPLE 2 PYRANTHRONE grams of pyranthrone are vatted at a temperature of 60 C. in a solution containing 33000. of sodium hydroxide (36 B.), 75 grams of sodium hydrosulfite and 100 grams of the sodium salt of ligninsulfonic acid in 3,500 cc. of water. The alkaline solution is slightly acidified with 100 cc. of acetic acid (30%) and the resulting col' loidal solution freed from impurities by filtration. The solution is then spray dried so as to obtain a dye in the form of a powder.

Pyranthrone is a typical hot dyeing color having a high rate of exhaustion. In a concentrated dyebath. cotton fibers absorb 65% of the dyestuff within two minutes, and the absorption rate on staple fiber is still higher, which makes it impossible to use concentrated vats of this dyestuff for dyeing loose staple fiber stock in the packing machine. The regenerated cellulose swells strongly in the alkaline bath and prevents the circulation of the dye liquor; therefore, the outer layers of the fiber stock will absorb so much of the dyestuff that uniform penetration-cannot be obtained even though levelling agents be used and the stock vat be added in batches.

Other special procedures do not ensure a satisfactory dyeing either, whereas the vat acid process according to the invention permits to prepare in a very short time the substantive alkaline leuco compound in high concentration but with such a low alkali concentration that the staple fiber swells only to a small extent.

The conventional vat acid' process with pyranthrone would be carried out as follows:

1.5 kg. of pyranthrone are vatted in '75 liters of water with 3 kg. of sodium lignin sulphonate, 5 1. of 36 B. sodium hydroxide solution and 1.13 kg. of sodium hydrosulfite at 60 C. for 10 minutes. To obtain the acid dispersion,the vat is then stirred into the dyebath at 60 C. which contains 3 l. of concentrated acetic acid. In this procedure, care has to be taken that the 10 minute limit is not exceeded in vatting; if the concentrated alkaline vat is allowed to stand for a longer period of time, crystallization takes place-which crystals cannot be dissolved even in strong solution-and structural changes of the reduced dyestuff take place which change the shade and fastness of the color.

The acid bath is then circulated through the fiber stock at 60 C. for -l0 minutes, and in intervals of 5 minutes there are added under continuous agitation 4 times 3.05 'l. of 36 B. NaOI-l, and .81 kg. of sodium hydrosulfite.

The dyeing is continued for 30 more minutes and then finished as usual.

In contradistinction to this known vat acid process where it is necessary to control and maintain exactly the time of the alkaline vatting, the process according to the invention eliminates completely this requirement.

All that the dyer in a textile mill has to do is to dissolve 7.5 kg. of a pyranthrone vat acidobtained as described in the first paragraph of this examplein the form of a powder or paste containing 20% of the dyestuff in 500 1. of water at 60 .C. and to circulate the dye liquor through the fiber stock for about minutes. In this stage of the process, no substantial swelling takes place because of the treatment in an acid medium and the goods is homogeneously penetrated by the dyestufi. Subsequently, caustic soda and sodium hydrosulfite are added in small batches-as in the conventional vat acid process-to cause thegradual absorption of the dyestuilf on the fiber without undue swelling. n

In this example, a goods liquor ratio of :1 is maintained, which corresponds to a concentration of the dyebath of g. dyestuir per 1 kg. of staple fiber and to a 3 coloring.

It will readily be noted that the new method brings out all advantages of the vat acid process while avoiding the difiicult manipulations and drawbacks of the known process.

EXAMPLE 3 N-DIHYDRO-l.1'-2.2'-ANrHRAQUINoNEAzINE 100 parts of this dyestufi are vatted for five minutes at a temperature of 60 C. in a solution containing 412 parts by volume of sodium hydroxide (36 B.), 112 parts of sodium hydrosulfite and 100 parts of a condensation product of napthalene sulphonic acid with formaldehyde in 12,500 parts of water. The concentration of the dyestuif in this solution is about 7 g./1. which is about the maximum concentration to be obtained. The alkaline solution is acidified with 280 parts by volume of formic acid (90%) and evaporated to give a paste with a solid content of 20% of vat acid. The paste is then finally milled in a colloid mill.

The end product is soluble or can easily be dispersed in water to form vats containing the dyestuff in the form of vat acid in concentrations up to 80 ./l.

EXAMPLE DIMETHOXYDIBENZANTHRONE 100 parts of a dimethoxydibenzanthrone as obtained in commerce are stirred with 63 parts of potassium carbonate, 39 parts of formaldehydesodium sulfoxylate, 43 parts of the condensation product of sodium napthalene sulfonate with formaldehyde, and 22 parts of water. The mixture is heated at 100 C. and then neutralized with 22 parts of glacial acetic acid. A product is obtained which contains about 20 per cent of free vat acid.

EXAMPLE 5 DI-ALPHA-AHTHRAQUINOYL-l'5 DIAMINOANTHRA- QUINONE AMIDE This grey color possesses excellent fastnesses, especially a fastness to mercerization exceeding almost all other grey colors, and is therefore very popular for producing pale grey shades in efiect dyeings. But its heat sensitivity even in vats of low dyestuif and very weak alkali concentrations is so high that it is converted by an intramolecular rearrangement into a brown shade when a temperature of 25 C. is exceeded during the dyeing procedure, which takes half to threequarters of an hour.

This drawback can be obviated by the following process where a solid vat acid composition is prepared as follows:

100 parts of di-alpha-anthraquinoyl-1-5' diaminoanthraquinone amide are vatted in 2,500 parts of water with 385 parts by volume of a 36 B. sodium hydroxide solution, 100 parts of sodium hydrosulfite, and 200 parts of a fatty alcohol sulphonate at C. for 5 minutes. The vat is then neutralized with 230 parts by volume of concentrated acetic acid and 500 parts of water and dehydrated to a paste containing about 10 per cent of the vat acid.

A vat is then prepared by dissolving 10 grams of the paste per liter of the dyebath and hank goods 4 are impregnated in batches of 1 kg. with said dispersion and uniformly squeezed. Each batch is dyed at 25 C. for 45 seconds. The dyeing is then developed by treatment with a solution containing 3 cc. of 36 B. sodium hydroxide, 2 grams of sodium hydrosulfite and. 10 grams of common salt per liter at 45 C. for a period of only 10 minutes. Subsequently, the goods is oxidized,

rinsed, soaped, and processed in the usual manner.

EXAMPLE 6 Bis DIPnsnrmrvnnAzoL or NAPHTHALENETETRA- CARBOXYLZC Acre ber of selected other vat dyes could be dyed on wool from an ammoniacal reduction bath without material injury to the fiber.

It is, however, possible to enlarge the color scale by vat dyes otherwise suitable only for vegetable fibers when the vat acid process is employed; here the alkaline development is limited to such a short period of time as to prevent substantial changes of the wool structure. Vat acid compositions in solid or paste form are particularly suitable for this purpose.

parts of bis-diphenylimidazol of naphtha- Ienetetracarooxylic acid are vatted with 500 parts by volume of a 36 B. sodium hydroxide solution, 100 parts or" sodium lignin sulphonate and parts of sodium hydrosulfite in 7,500 parts of water at a temperature of 60 C. for 10 minutes. The vat is then converted into free finely dispersed vat acid by addition of 300 parts by volume of acetic acid in 500 parts of water.

The

water is removed and the mixture is dried to a composition containing 12.5 per cent of vat acid.

For -dyeing kg. of wool yarn, 300 grams of said solid vat acid and 300 cc. of acetic acid are dissolved in 300 liters of cold water. The goods is put into the dyebath of which the temperature is raised to the boiling point in the course of half an hour. Then, the goods is boiled for minutes, whereupon the bath is allowed to cool down during 20 more minutes.

The yarn is developed in a bath containing 20 grams of calc. soda, 20 grams of sodium hydrosulfite and 5 grams of sodium lignin sulphonate per liter for one minute. Subsequently it is oxidized, rinsed, treated for minutes in an acetic acid bath of fatty alcohol sulphonate at a temperature of about 0., re-rinsed, and dryed in the usual manner.

EXAMPLE 7 TETRAhROMOINDIGO Indigo M2B/4B, Cz'ba Blue 2B, Schultz-Julius 1314, c. I. 1184 A very interesting application of the solid vat acids is presented by their use in the printing art. Printing pastes containing normal vat dyes require quite complicated procedures which have to be adapted in each case to the properties of the different dyestuffs and to the peculiarities of the development in the steambox. Therefore, the vat dyes have often been replaced by their leuco esters which are reconverted to the original dyestuff by acid splitting in the presence of an oxidizing agent. However, the selection of suitable leuco esters is rather restricted and the coloring is limited to a few shades.

The use of concentrated vat acid compositions offers an excellent solution of this problem. Such compositions can be printed with a thickener without further additions; after drying, the prints keep for unlimited periods of time, in contradistinction to the usual vat dye prints-made with an admixture of the unstable sodium sulfoxylate formaldehyde or of the mostly light sensitive leuco esters.

The vat acid may be prepared as follows:

parts of tetrabromoindigo' are vatted in 5,000 parts of water with 275 parts by volume of 36 B. sodium hydroxide solution, 100 parts of sodium hydrosulfite and 200 parts of the condensation product of napthalene sulphonic acid with formaldehyde at 70 C. for 5 minutes. The

vat is neutralized with a solution of parts by volume of concentrated acetic acid in 1000 parts of water. The obtained suspension is freed by dialysis from the excess of salt and dried to a product containing 25 per cent of vat acid.

100 grams of this product are dispersed in 350 rams of Water and mixed with 550 grams of a methyl cellulose thickener (60 21000) The obtained paste is printed out, the print is dried in the hot air chamber and padded in a bath containing 50 grams of hydrosulfite and 50 cc. of 36 B. sodium hydroxide solution.

Subsequently the print is steamed in the rapid ager at about 102 C. for 2 to 3 minutes, rinsed, oxidized, soaped, re-rinsed, and finished in the usua1 manner.

It Will be apparent tothose skilled in the art that the invention will be susceptible of many variations without departing from the essence of the invention and all such variations are intended to be included within the scope of the following claim.

What I claim is:

A method of preparing concentrated free vat acids from difiicultly soluble vat dyestuffs comprising the steps of mixing a vat dyestulf with alkali and a reducing agent to a dispersion containing water in an amount insufficient to dissolve the dyestuff, reducing the dyestuff in said partly undissolved state to its leuco compound, and adding an acid agent in an amount sufficient to form the free vat acid, thereby obtaining the readily soluble vat acid of said vat dyestufif in fine dispersion.

' GEORGE N. SANDOR.

DES CHTED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 21,402 Crossley Mar. 19, 1940 1,141,148 Schmidt June 1, 1915 1,900,172 Ellis Mar. '7, 1933 1,930,409 Barnes Oct. 10, 1933 2,107,526 Dreyfus Feb. 8, 1938 2,193,751 Wenk Mar. 12, 1940 2,227,834 Kacer 1 Jan. '7, 1941 FOREIGN PATENTS Number Country Date 358,439 Great Britain Mar. 31, 1930 

